Abstract
We experienced a woman in her 70s showing bilateral blepharoptosis with diurnal fluctuation. Positive neurological finding was right dominant bilateral blepharoptosis which worsened towards the evening. There was no weakness in the other skeletal muscles in the cranial nerve areas, limbs, and body trunk. Serum anti-acetylcholine receptor (AchR) antibody was positive. Chest X-ray computed tomography showed thymoma in the anterior mediastinum. A clinical diagnosis was ocular type myasthenia gravis (MG). We performed a lower frequency repetitive nerve stimulation test (RNS) on the right nasalis, trapezius, abductor digiti minimi, and the anconeus muscles as well. The results showed no waning phenomenon in the nasalis, trapezius, abductor digiti minimi muscles but in the anconeus muscle. The anconeus muscle is noticed as the target muscle for RNS. A waning phenomenon is reported to be less sensitive in the limb or truncal skeletal muscles in ocular type MG. The facial muscle is regarded as a better target for detecting a waning phenomenon with better sensitivity, but our case showed no waning phenomenon even in the facial muscle. Our result suggested that the anconeus muscle should be considered as a target of RNS to improve sensitivity in clinical diagnosis of ocular type MG.
